The present invention relates to methods for calculating blood pressure of an artery. In addition, the present invention relates to a method for ascertaining a relationship between at least one preselected parameter of at least one sensed pressure waveform and a blood pressure value for use in determining the blood pressure value.
Blood pressure has been typically measured by one of four basic methods: invasive, oscillometric, auscultatory and tonometric. U.S. patent application Ser. No. 08/388,751, entitled "METHOD AND APPARATUS FOR CALCULATING BLOOD PRESSURE OF AN ARTERY" and U.S. patent application Ser. No. 08/227,506 entitled "CONTINUOUS NON-INVASIVE BLOOD PRESSURE MONITORING SYSTEM", both of which are assigned to Medwave, Inc. (herein incorporated by reference), describe a novel non-invasive method for continuously measuring blood pressure without causing discomfort to a patient. The novel method involves non-invasively sensing amplitude and shape of the blood pressure pulses within the underlying artery to create signals representing the amplitude of the sensed blood pressure pulses. Based upon the sensed signals representing the sensed amplitude and shape of the blood pressure pulses, wave shape information is determined by measuring the amplitude and shape versus time of individual cardiac cycles. Parameter values derived from the sensed signals and the wave shape information are used by a microprocessor to calculate systolic, diastolic and mean blood pressures. However, it has been extremely difficult to ascertain a single function that accurately predicts blood pressure values based upon the derived parameter values. As a result, the use of a single function to calculate blood pressure values from the derived parameters has been extremely error prone.